[mercury-users] existential type question

[Peter Ross]

stayl wrote:
> On 30-Nov-2002, Peter Ross <peter.ross at miscrit.be> wrote:
> > % mmc -e arg2.m
> > arg2.m:022: In clause for predicate `arg2:p/2':
> > arg2.m:022:   in unification of variable `MaybeArg'
> > arg2.m:022:   and term `arg(Arg)':
> > arg2.m:022:   type error in argument(s) of functor `arg/1'.
> > arg2.m:022:   Argument 1 (Arg) has type `(some [T] T)',
> > arg2.m:022:   expected type was `(some [U] U)'.
> > For more information, try recompiling with `-E'.
>  
> > :- type maybe_arg
> > ---> some [U] arg(U)
> > ; no.
> > 
> > :- pred p(t::in, maybe_arg::out) is cc_multi.
> > 
> > p(I, MaybeArg) :-
> > q(I, Univ),
> > Arg = univ_value(Univ),
> > MaybeArg = arg(Arg).
>  
> Shouldn't that be
>   MaybeArg = 'new arg'(Arg).

Doh!!!!  That is all it is.  Thanks.


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